| Purified flint-sand (or glass-powder) | 10 |
| Caseine or curd | 8 |
| Slacked lime | 10 |
Mix thoroughly, and add water to a creamy consistency.
The following for metals is also very strong:—
| Sturgeon’s bladder solution | 100 |
| Nitric acid | 1 |
The acid is stirred in at the same time with the cement, which should be as dense as possible, and with this mixture the surfaces of the metal are covered. “The nitric acid is intended to make the surfaces of the metal rough, but it has the drawback that it hinders the drying of the glue” (Lehner). This slowly drying is, however, a great advantage. The same is found when it is mixed with common glue, which generally dries too rapidly. Cements which dry rather slowly take hold the most firmly and permanently. The acid hardens the mass by contracting the cellular tissue. To hasten the drying, the metallic parts, which should be very strongly compressed together, must be exposed to heat.
A simpler method for light articles of metal is to wet the surfaces with nitric acid for a few minutes till they are roughened, then wash away the acid in water, and cement the metal with sturgeon’s bladder cement.
A special cement for zinc is made by thickening very strong dense glue with powdered slacked lime, into which is kneaded one-tenth part of flowers of sulphur.
A so-called Jeweller’s Cement, which holds firmly, is the so-called Diamond, elsewhere given; also the following:—
| Sturgeon’s bladder | 100 |
| Gum mastic varnish | 50 |
The sturgeon’s bladder is dissolved in as little water as possible with strong spirits of wine (equivalent to ordinary spirits). To prepare the mastic varnish, mix finely powdered mastic with the most highly rectified spirits of wine and benzine, and use as little liquid as possible. The two mixtures must be then rubbed as intimately as possible together. When carefully made this cement will serve for anything—glass or china, &c.